The development of advanced materials has accelerated in recent years. Materials of various types have properties that are desirable for a wide range of applications in diverse environments. Although the materials are highly advanced, it is often difficult to adapt them for use in applications in which they must interface with materials having different properties. Sealing of dissimilar materials at interface surfaces between the materials, for example, has frequently been problematic.
Many applications require materials to be sealed hermetically. Providing reliable hermetic seals at the interface surfaces of materials having different properties, particularly different coefficients of thermal expansion, has been difficult. U.S. Pat. Nos. 5,298,683, 5,433,260, 5,675,122, 5,110,307, 5,041,019, 5,109,594 and 4,690,480 disclose various methods for hermetically sealing different types of materials, particularly materials having different thermal properties, to one another. Many of these patents relate to hermetically sealing various materials for use in electrical connectors and electronics packages using a transition joint or bushing.
U.S. Pat. No. 4,991,582 discloses a sealed ceramic and metal package for electronic devices implantable in living bodies. This patent describes a device in which a ceramic sleeve is sealed to a metallic band having substantially the same coefficient of linear thermal expansion. The sleeve is formed of an inert ceramic material such as alumina or boron nitride, and the metal band is formed of niobium, molybdenum or tantalum. A header plate carrying a substrate on which the electronic components are mounted and having a plurality of electrical connectors is then sealed to the metal band. The ceramic sleeve is sealed to the metal band employing a butt brazing technique using an alloy of 71.5% titanium and 28.5% nickel. Brazing is accomplished by heating the ceramic sleeve, fitted with the metal band and an annular foil of brazing material. The electronic components that are ultimately mounted in the ceramic sleeve cannot tolerate the high temperatures required during the brazing operation, and are inserted into the cavity formed by the ceramic sleeve when the header is joined to the metallic band. The metal to metal seal between the header and the metal band is provided using high temperature welding, such as laser or electron beam welding, having a low heat-affected zone that does not affect the integrity of the electronic components.
U.S. Pat. No. 3,594,895 discloses 50-50 brazing alloys of titanium with iron, cobalt, nickel or mixtures thereof for sealing ceramic to metallic materials, such as tantalum, niobium and group VIII metals. The 50-50 titanium-niobium brazing alloy had a melting point of 1250.degree. C., requiring heating to temperatures just above 1250.degree. C. for brazing. The brazing process, including the heating, melting and cooling process, took about five minutes.
Zirconia ceramic materials and, particularly, stabilized zirconia ceramic materials, are preferred ceramic materials for many applications. Zirconia ceramics are generally stronger and less reactive in harsh environments than alumina ceramics, making them suitable candidates for applications such as implantable devices. The relative expense of zirconia ceramics and the difficulty of providing reliable hermetic seals at the interface of zirconia ceramics with metallic materials have presented challenges in using zirconia ceramics in many applications. Providing a reliable hermetic seal of zirconia ceramic materials to metallic materials, and particularly titanium-containing metallic materials, has been particularly difficult as a result of the active nature of titanium metals. The methods of the present invention are directed to providing reliable, hermetic seals at the interface of ceramic materials, particularly zirconia ceramic materials, with metallic materials, particularly titanium-containing metallic materials.